F3: The transient catastrophic Universe

The capability to study transient phenomena on time scales from milliseconds to years has recently increased and shown large discovery potential. Yet, the time domain of the sky has been sparsely explored. Fermi and Swift are now showing the way at high energies, the former by mapping the whole sky every 3 hours, the latter by its rapid follow-up across many wavelengths.With the construction of wide field imagers dedicated to sky surveys on a daily timescale in the radio (Lofar, ASKAP, MeerKAT), optical (Pan-STARRS, LSST), infrared (Akari), and X-ray (eRosita/SRG), and with the ongoing surveillance in gamma rays from Fermi, there are new motivations to explore transients. Discovering new classes of fast transients is one, as it could represent new exotic or explosive events out to cosmological distances, such as merging neutron stars or evaporating black holes.

Over the next decade, a combination of increased sensitivity, larger field of view, and algorithmic developments will open up the time domain to a wide range of astronomical fields, from stellar flares and supernovae to neutron-star and black-hole births, quakes and instabilities. Near-coincidence searches with high-energy neutrino and gravitational wave signals will be actively pursued across the world. The dynamic and bursting events represent the new terra incognita.

Radio astronomy is leading this effort. Transient science is identified as a key goal for LOFAR (Europe), ASKAP (Autralia) and MeerKAT (South Africa) that are the precursor instruments of the major international SKA facility to be developed for the 2020+. The synchrotron radio emission probes with unequalled angular resolution the cooling in the ambient magnetic field of the relativistic particles ejected by compact accretors or explosions. It also constrains the kinetic feedback of such events on their environment.

Artistic view of a small part of the SKA kilometer array (a decision regarding the selection of the SKA site is expected in the next months).

Algorithmic improvements for transient detection would yield improved use of the different combinations of fields-of-view and unprecedented sensitivities offered by these instruments. The vast storage and computational requirements of transient searches, in particular for imaging interferometers, also requires the development of near real-time detection pipelines. The LOFAR project is engaged in the development of first-generation pipelines. The characterization of transients and their identification at other wavelengths represents another challenge.

LOFAR is a radio telescope currently being built in The Netherlands and neighboring countries

Image from one of the Lofar low frequency station in Nançay (France)

POSITION

NAME SURNAME

LABORATORY NAME

GRADE, EMPLOYER

WP leader

Corbel Stéphane

AIM

Professor, University Paris Diderot

WP co-leader

Grenier Isabelle

AIM

Professor, University Paris Diderot

WP co-leader

Starck Jean-Luc

AIM

Researcher/CEA

WP member

Girard Julien

AIM

Ass. Prof., University Paris Diderot

WP member

Migliori Giulia

AIM

Post-doc, LabEx UnivEarthS (Dec 14-Dec 17)

WP member

Loh Alan

LESIA

Post-doc at LESIA/OP (former AIM PhD)

WP member

Jiang Ming

AIM

PhD Student (Start Oct 14)

WP member

Evangelia Tremou

AIM

New post-doc (Start Nov 17)

WP member

Floriane Cangemi

AIM

New PhD Student (Start Oct 17)

WP member

Pires Sandrine

AIM

Researcher/CEA

WP member

Bobin Jérôme

AIM

Researcher/CEA

WP member

Rodriguez Jérôme

AIM

Researcher/CEA

In collaboration with Cyril Tasse (GEPI, Observatoire de Paris) and the LOFAR (TKP), MeerKAT (ThunderKAT) and ASKAP(VAST) collobarations

2016 Milestones:

Deconvolution algorithm (SASIR) was implemented in the new radio imager DDFacet which is the most advanced analyse tool actually. In parallel, development of two extensions (temporal and spectral) for the reconstruction of the temporal and spectral profile of radio sources.

First detection at high energies with Fermi/LAT of the transitory gamma ray emission of an accreting small mass black hole (Loh et al. 2016) and of a new class of AGN (Migliori et al. 2016).

First detection of a radio transitory at low frequency with LOFAR (Stewart et al. 2016).

Many publications regarding the variability of the behavior of compact sources

The SKA pathfinders

LOFAR

Core located in The Netherlands, with international stations located in France, UK, Germany and Sweden

Now operational

MeerKAT

64 antennas of 13.5 m to be operating from 0.6 to 15 GHz

Location: South Africa

Completion: 2016-18

KAT-7

7 dishes to be used as a MeerKAT precursor. 0.9 to 1.6 GHz

Location: SOuth Africa

Now operational

ASKAP

36 antennas of 12-m diameter located in Western Australia operating around 1.4 GHz. Large field of view.